The present invention relates to an asynchronous transfer mode (ATM) network. More particularly, the present invention relates to a server address management system in an ATM network for managing the addresses of communication terminals due to the nonbroadcast nature of the ATM network.
Currently, a network for connecting computers so that they communicate data to each other is widely used. Such a network is, for example, a local area network (LAN) which is used in an office and other environments on a relatively small scale and the Internet which is used between companies or nations on a relatively large (world-wide) scale. As these networks cannot directly communicate with a public network such as telephone lines, they have been widely used independent of the public network.
Recently an asynchronous transfer mode (ATM) which will enable direct communication between the above-described networks and a public network has been researched and developed. A network operated according to an ATM (hereinafter called ATM network) is a nonbroadcast system in which broadcast communication is not possible different than existing LAN's such as Ethernet (the registered trademark of Xerox Corporation).
FIGS. 2 to 6 illustrate an example in which in a nonbroadcast system the terminals do not know the identifier (hereinafter called address) used for communication between the terminals. First, referring to FIG. 2, system configuration will be described. A terminal A 201 is an information processing system such as a personal computer (PC) and a workstation (WS) for managing the address of terminals (terminals B 203 and C 204 in this example) in a system and ADDR1 is allocated to the terminal A as its address. The terminal A is provided with an address table 206 illustrated in FIG. 3 in which a terminal name 301 (IP address in TCP/IP network) and a terminal address 302 are stored and functions as an address server.
The terminals B 203 and C 204 are information devices such as a PC or a WS which communicate with another terminal in the system and ADDR2 and ADDR3 are respectively allocated as their addresses. SW 202 is communication equipment for connecting terminals in the system via communication wire 207 and switching a communication path and is equivalent to a switching system in a public network. The communication wire 207 connects each terminal and SW 202. A twisted pair cable or an optical fiber are examples of communication wire 207.
Next, referring to FIGS. 4 to 6, an example in which the terminal B 203 communicates with the terminal C 204 will be described. This example is known as address resolving as described in "Classical IP and ARP over ATM", by M. Lauback, Internet Engineering Task Force, Network Working Group Request for Comments; 1577 Category: Standards Track, January 1994, pp 1-17.
As the terminal B 203 not provided with an address table does not know the address of another terminal in the system, it cannot communicate with the other terminal. The reason why only the address server 201 is provided with the address table 206 is that if an address table is distributed, it is difficult to match table information and that in the case of a large-scale system including many terminals, a workload for generating a table is enormous.
Therefore, the terminal B 203 inquires of the address of the terminal C 204 to the address server 201 which manages an address. However, as the terminal B 203 does not also know the address of the address server 201 while it is activated, any of the following three methods is executed:
(1) An operator enters the address (ADDR1) of the address server 201 in the terminal B 203 as shown in FIG. 4. PA1 (2) The address of the address server 201 is stored in the terminal B 203 and the address is used. PA1 (3) The terminal B 203 communicates using a fixed address (a well-known address) and SW 202 converts it to the actual address of the address server 201.
In an ATM network the above methods (1) and (2) are mainly used and method (3) is used for LAN emulation which is one of the communication modes of ATM network. The terminal B 203 which obtains the address of the address server 201 according to the above method requests the address server 201 to provide to it the address of the terminal C 204.
The address server 201 which receives the request checks the address table 206 and sends ADDR3 which is the address of the terminal C 204 to the terminal B 203 as a response as shown in FIG. 5. The terminal B 203 which receives the address (ADDR3) of the terminal C 204 communicates with the terminal C 204 using the address as shown in FIG. 6.
The above example illustrates the following problems which exist in conventional technology.
(1) When the address of an address server is entered manually in each terminal, the work load of the operator increases in proportion to the number of terminals.
(2) If plural address servers are added to a system when the address of a particular address server is stored or a well-known address is used, the added address servers cannot be selected until modifications to the system are made.
(3) If a failure occurs in an address server, another terminal cannot take over the function of the failed address server as a substitute server until the address of the substitute server has been registered in each terminal.